This invention is generally directed to a novel venting structure formed in a headlamp adjustor mechanism for venting an automotive headlamp arrangement. More particularly, the invention contemplates a venting structure which is incorporated into the design of a headlamp adjustor mechanism to vent pressure and moisture laden air from the inside of the headlamp arrangement to the atmosphere while allowing the passage of air and a minimal amount of moisture, if any, back into the inside of the headlamp arrangement to equalize internal pressures with atmospheric pressure.
Headlamp arrangements commonly used on automobiles today consist of a moveable headlamp component, such as a reflector member or the like, which is housed in a stationary component connected to the frame of the automobile. The stationary component is sealed to prevent the entrance of dirt, contaminants and moisture into the headlamp arrangement. An adjustor mechanism is provided through an aperture in the stationary component and is used to effect pivotal movement of the reflector member.
The adjustor mechanism includes a housing member which is sealed to the stationary component, and an adjusting screw member which is housed in an axial bore through the housing member. An end of the adjusting screw engages the moveable headlamp component to effect pivotal motion of the component when the screw is moved. The adjustor mechanism is sealed so as to prevent the entrance of moisture inside of the stationary component so as to prevent interference with the workings of the movable headlamp component.
Despite the fact that the headlamp arrangement is sealed to prevent the entrance of moisture therein, water often accumulates inside of the headlamp arrangement. This occurs because of microcracks in the joints between the components which are caused by stress over time which allow moisture to seep into the headlamp arrangement. As a result, sealed or improperly ventilated headlamp arrangements often eventually fail to keep the moisture out of the arrangement which can cause interference with the functioning of the headlamp.
The microcracks occur due to pressure differences encountered in use together with thermal expansion and contraction of the housing material. As such, when the headlamp is turned on, the air inside the headlamp is heated by the energized bulb in the headlamp which causes the air trapped in the lamp housing to expand and the pressure inside the sealed headlamp arrangement to build up. This, of course, is in addition to the thermal expansion caused by such heat. The force due to the pressure build up persists until the bulb is turned off. As the headlamp is turned on and off over time, the joints between the components eventually crack due to the pressure extremes and the expansion and contraction of the components.
During the time period when the bulb in the headlamp is on, the air from inside the headlamp leaks through the microcracks which slowly reduces the pressure inside the headlamp arrangement to atmospheric conditions. When the bulb is turned off, an equal amount of air must be allowed to pass back into the headlamp arrangement so that the air pressure inside the headlamp arrangement can equalize with atmospheric. Since the cracks are too small to allow for the free flow of air therethrough, a negative pressure condition persists as air slowly enters into the headlamp through the cracks. Under these conditions, if the headlamp arrangement is subjected to wet weather conditions, moist air and/or water droplets are drawn into the headlamp arrangement.
The headlamp arrangement does not usually eliminate the moisture inside of the arrangement when the headlamp is turned on again. Over time, an appreciable amount of water builds up within the headlamp arrangement.
To eliminate, or to at least substantially minimize, the entrance of moisture into the headlamp arrangement during energization of the bulb, moveable reflector headlamps are vented to decrease the pressure build up inside the headlamp and to allow the moisture which has entered into the headlamp arrangement to exit the arrangement. Specifically, the vents allow moisture and air pressure out of the headlamp and only air and a limited amount of moisture into the headlamp. These vents are typically formed as a small hole, a rubber diaphragm or a microporous meshed filter.
One such microporous filter, which uses a non-woven hydrophobic membrane made of Gore-tex.RTM., is manufactured by Filtertek, Inc. Gore-tex.RTM. is a registered trademark of W. L. Gore & Associates, Inc. The filter is housed in a tube-like body member which is attached to an orifice in the stationary headlamp component. A cap snaps over the end of the tube-like body, but does not seal the end of the tube-like body, to protect the microporous filter from dirt, dust or other particles.